This invention relates to new and useful improvements in machines for testing and comparing chain and sprocket geometries, materials, and lubricants. Moreover, the invention relates to a machine for testing and comparing not only chains and sprockets but also timing belts and timing belt pulleys of various materials and geometries. The machine also has versatility for using different lubrication systems and for simulating various environmental conditions. More particularly, the invention relates to a machine that employs a pneumatic system for applying force to the chain drive machine elements.
Chains and sprockets or timing belts and timing belt pulleys are used wherein the transmitted motion from one shaft to another needs to be in an exact ratio, such as for precise timing in various machines. Power capacity at various loads and speeds is a primary factor in selecting a roller chain and sprocket for a particular application. Power capacity for chains is generally expressed in terms of the number of teeth and rpm on the smallest sprocket running in mesh with the chain. Its power capacity is expressed for a given life, generally 10,000 hours, with a 180 degree angle of wrap. Sprocket rpm is measured using a strobotac. Chain speeds are normally expressed in feet per minute and computed as the product of the sprocket pitch circumference in inches times the revolutions per minute of said sprocket divided by 12. For chains operating under conditions of boundary lubrication, or dry lubrication, there is a direct relationship between the speed and load that can be carried by any chain material. The greater the load, the less the allowable speed, and conversely the greater the speed, the less the allowable load.
The present invention relates generally to the field of chain wear measurement or chain and sprocket fatigue testing and in particular to a method and apparatus for determining the power capacity of a chain and sprocket drive system for a given life. The method and apparatus also is used in measuring or testing the effectiveness of chain drive lubricants. Test machines for determining chain and sprocket system power capacity are known to the prior art. They generally operate by loading one chain strand against another through the application of an external force. This type of machine is described in the prior art as a four-square tester. Power is required only to overcome the frictional resistance in the machine itself.
While four-square machines are to some extent well known in the industry, these devices are inaccurate when measuring chain loads, speeds, and determining power capacities of chains and sprockets. Dynamic loads are not equal to loads applied to the chains; and sprocket misalignment is common. Furthermore, the known four-square machines generally employ weights in order to apply the external load or they utilize friction slides which distract from the accuracy of the chain and load measurement.
The present invention is directed to an advanced method and apparatus for measuring or testing horsepower capacity of chain drive systems, which overcome the disadvantages and drawbacks of known prior art techniques.